The present invention relates to a method and device for detecting the position of terminals and/or edges of components, wherein an imaging camera is employed.
In the automatic insertion or assembly of printed boards or ceramic substrates with SMD components, the individual components are removed from a magazine or a delivery means using an insertion head and are then positioned in a prescribed position on the printed board or the ceramic substrate. Since the components have a positional tolerance of approximately 1 millimeter in the magazine or in the pick-up position of a delivery means, yet require highly exact positioning on the printed board or the ceramic substrate, an automatic position detection and correction is necessary. The position detection should require as little time as possible in order to enable a high insertion performance (throughput) of the insertion machine.
Known arrangements for detecting the position of the terminals and/or of the edges of components form images of the component or parts of the component, on a planar CCD camera via an objective and detect the position of the terminals of the component by means of digital image processing. The position of the component is subsequently corrected prior to placement with the aid of a transport device at which the component is secured at the insertion head. In practice the method is also designated as optical centering of the component.
PCT Application WO 93/19577 teaches a method for position detection wherein an immediate casting of shadows of the terminal region of a side of a component is created on the photosensitive surface of a spatially resolving opto-electronic transducer or converter (as a camera). The opto-electronic transducer is therein secured at the insertion head, and the position of the terminals is determined with reference to the opto-electronic transducer. The position of the terminals with reference to the insertion head is determined by a known relative position of the opto-electronic transducer relative to the insertion head. In his method, it is assumed that the position of the camera relative to the transport device is known exactly and that it can be approached exactly. Any errors due to a drift of the camera location or due to transient processes in the approaching of the camera position enter into the measurements as errors. Thus it is necessary to wait until the transport device has come to a halt.
Methods are also known in which a photographing or image pick-up of the component ensues with very short exposure time (flash operation) during a continuous motion of the transport device with the component. At the time of the imaging, the position of the transport device relative to the camera is determined by counting rotations of the axis of the transport device. Given errors between the count and the actual position of the transport device, the determination of the relative position between component and transport device in this method is also impeded.
It is an object of the present invention to provide a method and a device which guarantee a more precise and a faster detection of the position of components with reference to the transport device.
The above object is achieved in accordance with the principles of the present invention in a method and device for detecting the position of terminals and/or edges of components with reference to a transport device with which the components are detachably held wherein the transport device has at least one position marking fixedly connected thereto and wherein a camera obtains an image of the position marking, together with the terminals and/or edges of the component held by the transport device. An evaluation unit, supplied with the aforementioned image obtained by the camera, identifies the relative position between the terminals and/or the edges, and the position marking. The relative position between the terminals and/or the edges and the transport device can then be determined from the relative position identified from the image.
By a common imaging of position markings connected securely with the transport device and of the terminals and/or of the edges of the components, the relative position between the transport device and the terminals and/or the edges of the components is determined in the image evaluation unit without knowledge of the exact position of the camera, whereby a more exact detection of position is guaranteed. Transient processes have no influence on the precision, since they affect the position markings and the terminal and/or the edge in the same way.
In an embodiment of the method and device, the position markings are connected to the transport device such that they are arranged in the immediate vicinity of the terminals and/or the edges, so that they lie in a common depth-of-field region of the camera along with the terminals and/or the edges and are picked up with equal sharpness.
In a preferred embodiment of the method and device, the position markings are imaged by an optical imaging in the immediate vicinity of the terminals and/or the edges, so that the environment of the terminals and/or the edges is kept free of costly structures.
The imaging can ensue on a ground-glass screen in the immediate vicinity of the terminals and/or the edges, which simplifies the photographing or pick-up of the image by the camera.
A more rapid completion of the position detection of the components is achieved when the imaging ensues with short exposure time and thus also during the motion of the transport device.